I don't know much about cdb but:
there seems to be a bug in the debugger-plugin when you reopen a project and the Build target is "Debug".
Even if it's chosen in toolbar C::B might use another Build target when you start the debugger.
In this case you can change your Build target to (for example) "Release" and then go back to "Debug" and try it again.
If that does not work, you can turn on the debuggers log under "Settings -> Compiler and debugger settings -> Debugger settings" with the appropriate checkbox.
You should than have a new Tab in the log area called "Debugger (debug)" where the commands send to the debugger and the feedbacks go.
This might help you (or somebody here) to find what's wrong.